Not Applicable
The present invention relates to the field of methods and devices for the embolization of vascular aneurysms and similar vascular abnormalities. More specifically, the present invention relates to an embolic device that is inserted into a vascular site such as an aneurysm to create an embolism therein and a method for embolizing a vascular site using the device.
The embolization of blood vessels is desired in a number of clinical situations. For example, vascular embolization has been used to control vascular bleeding, to occlude the blood supply to tumors, and to occlude vascular aneurysms, particularly intracranial aneurysms. In recent years, vascular embolization for the treatment of aneurysms has received much attention. Several different treatment modalities have been employed in the prior art. U.S. Pat. No. 4,819,637xe2x80x94Dormandy, Jr. et al., for example, describes a vascular embolization system that employs a detachable balloon delivered to the aneurysm site by an intravascular catheter. The balloon is carried into the aneurysm at the tip of the catheter, and it is inflated inside the aneurysm with a solidifying fluid (typically a polymerizable resin or gel) to occlude the aneurysm. The balloon is then detached from the catheter by gentle traction on the catheter. While the balloon-type embolization device can provide an effective occlusion of many types of aneurysms, it is difficult to retrieve or move after the solidifying fluid sets, and it is difficult to visualize unless it is filled with a contrast material. Furthermore, there are risks of balloon rupture during inflation and of premature detachment of the balloon from the catheter.
Another approach is the direct injection of a liquid polymer embolic agent into the vascular site to be occluded. One type of liquid polymer used in the direct injection technique is a rapidly polymerizing liquid, such as a cyanoacrylate resin, particularly isobutyl cyanoacrylate, that is delivered to the target site as a liquid, and then is polymerized in situ. Alternatively, a liquid polymer that is precipitated at the target site from a carrier solution has been used. An example of this type of embolic agent is a cellulose acetate polymer mixed with bismuth trioxide and dissolved in dimethyl sulfoxide (DMSO). Another type is ethylene vinyl alcohol dissolved in DMSO. On contact with blood, the DMSO diffuses out, and the polymer precipitates out and rapidly hardens into an embolic mass that conforms to the shape of the aneurysm. Other examples of materials used in this xe2x80x9cdirect injectionxe2x80x9d method are disclosed in the following U.S. Pat. No. 4,551,132xe2x80x94Pxc3xa1sztor et al.; U.S. Pat. No. 4,795,741xe2x80x94Leshchiner et al.; U.S. Pat. No. 5,525,334xe2x80x94Ito et al.; and U.S. Pat. No. 5,580,568xe2x80x94Greff et al.
The direct injection of liquid polymer embolic agents has proven difficult in practice. For example, migration of the polymeric material from the aneurysm and into the adjacent blood vessel has presented a problem. In addition, visualization of the embolization material requires that a contrasting agent be mixed with it, and selecting embolization materials and contrasting agents that are mutually compatible may result in performance compromises that are less than optimal. Furthermore, precise control of the deployment of the polymeric embolization material is difficult, leading to the risk of improper placement and/or premature solidification of the material. Moreover, once the embolization material is deployed and solidified, it is difficult to move or retrieve.
Another approach that has shown promise is the use of thrombogenic microcoils. These microcoils may be made of a biocompatible metal alloy (typically platinum and tungsten) or a suitable polymer. If made of metal, the coil may be provided with Dacron fibers to increase thrombogenicity. The coil is deployed through a microcatheter to the vascular site. Examples of microcoils are disclosed in the following U.S. Pat. No. 4,994,069xe2x80x94Ritchart et al.; U.S. Pat. No. 5,133,731xe2x80x94Butler et al.; U.S. Pat. No. 5,226,911xe2x80x94Chee et al.; U.S. Pat. No. 5,312,415xe2x80x94Palermo; U.S. Pat. No. 5,382,259xe2x80x94Phelps et al.; U.S. Pat. No. 5,382,260xe2x80x94Dormandy, Jr. et al.; U.S. Pat. No. 5,476,472xe2x80x94Dormandy, Jr. et al.; U.S. Pat. No. 5,578,074xe2x80x94Mirigian; U.S. Pat. No. 5,582,619xe2x80x94Ken; U.S. Pat. No. 5,624,461xe2x80x94Mariant; U.S. Pat. No. 5,645,558xe2x80x94Horton; U.S. Pat. No. 5,658,308xe2x80x94Snyder; and U.S. Pat. No. 5,718,711xe2x80x94Berenstein et al.
The microcoil approach has met with some success in treating small aneurysms with narrow necks, but the coil must be tightly packed into the aneurysm to avoid shifting that can lead to recanalization. Microcoils have been less successful in the treatment of larger aneurysms, especially those with relatively wide necks. A disadvantage of microcoils is that they are not easily retrievable; if a coil migrates out of the aneurysm, a second procedure to retrieve it and move it back into place is necessary. Furthermore, complete packing of an aneurysm using microcoils can be difficult to achieve in practice.
A specific type of microcoil that has achieved a measure of success is the Guglielmi Detachable Coil (xe2x80x9cGDCxe2x80x9d), described in U.S. Pat. No. 5,122,136xe2x80x94Guglielmi et al. The GDC employs a platinum wire coil fixed to a stainless steel delivery wire by a solder connection. After the coil is placed inside an aneurysm, an electrical current is applied to the delivery wire, which electrolytically disintegrates the solder junction, thereby detaching the coil from the delivery wire. The application of the current also creates a positive electrical charge on the coil, which attracts negatively-charged blood cells, platelets, and fibrinogen, thereby increasing the thrombogenicity of the coil. Several coils of different diameters and lengths can be packed into an aneurysm until the aneurysm is completely filled. The coils thus create and hold a thrombus within the aneurysm, inhibiting its displacement and its fragmentation.
The advantages of the GDC procedure are the ability to withdraw and relocate the coil if it migrates from its desired location, and the enhanced ability to promote the formation of a stable thrombus within the aneurysm. Nevertheless, as in conventional microcoil techniques, the successful use of the GDC procedure has been substantially limited to small aneurysms with narrow necks.
Still another approach to the embolization of an abnormal vascular site is the injection into the site of a biocompatible hydrogel, such as poly (2-hydroxyethyl methacrylate) (xe2x80x9cpHEMAxe2x80x9d or xe2x80x9cPHEMAxe2x80x9d); or a polyvinyl alcohol foam (xe2x80x9cPAFxe2x80x9d). See, e.g., Horak et al., xe2x80x9cHydrogels in Endovascular Embolization. II. Clinical Use of Spherical Particlesxe2x80x9d, Biomaterials, Vol. 7, pp. 467-470 (Nov., 1986); Rao et al., xe2x80x9cHydrolysed Microspheres from Cross-Linked Polymethyl Methacrylatexe2x80x9d, J. Neuroradiol., Vol. 18, pp. 61-69 (1991); Latchaw et al., xe2x80x9cPolyvinyl Foam Embolization of Vascular and Neoplastic Lesions of the Head, Neck, and Spinexe2x80x9d, Radiology, Vol. 131, pp. 669-679 (June, 1979). These materials are delivered as microparticles in a carrier fluid that is injected into the vascular site, a process that has proven difficult to control.
A further development has been the formulation of the hydrogel materials into a preformed implant or plug that is installed in the vascular site by means such as a microcatheter. See, e.g., U.S. Pat. No. 5,258,042xe2x80x94Mehta. These types of plugs or implants are primarily designed for obstructing blood flow through a tubular vessel or the neck of an aneurysm, and they are not easily adapted for precise implantation within a sac-shaped vascular structure, such as an aneurysm, so as to fill substantially the entire volume of the structure.
U.S. Pat. No. 5,823,198xe2x80x94Jones et al. discloses an expansible PVA foam plug that is delivered to the interior of an aneurysm at the end of a guidewire. The plug comprises a plurality of pellets or particles that expand into an open-celled structure upon exposure to the fluids within the aneurysm so as to embolize the aneurysm. The pellets are coated with a blood-soluble restraining agent to maintain them in a compressed state and attached to the guidewire until delivered to the aneurysm. Because there is no mechanical connection between the pellets and the guidewire (other than the relatively weak temporary bond provided by the restraining agent), however, premature release and migration of some of the pellets remains a possibility.
There has thus been a long-felt, but as yet unsatisfied need for an aneurysm treatment device and method that can substantially fill aneurysms of a large range of sizes, configurations, and neck widths with a thrombogenic medium with a minimal risk of inadvertent aneurysm rupture or blood vessel wall damage. There has been a further need for such a method and device that also allow for the precise locational deployment of the medium, while also minimizing the potential for migration away from the target location. In addition, a method and device meeting these criteria should also be relatively easy to use in a clinical setting. Such ease of use, for example, should preferably include a provision for good visualization of the device during and after deployment in an aneurysm.
Broadly, an embolization device, according to a first aspect of the present invention, comprises one or more expansible, hydrophilic embolizing elements non-releasably carried along the length of a filamentous carrier. In a first preferred embodiment, the carrier is a suitable length of very thin, highly flexible filament of nickel/titanium alloy (Nitinol). A plurality of embolizing elements are spaced along the length of the carrier and are separated from each other on the carrier by radiopaque spacers in the form of highly flexible microcoils made of platinum or platinum/tungsten alloy, as in the thrombogenic microcoils of the prior art, as described above.
In a second preferred embodiment, the carrier comprises a continuous length of highly flexible, hollow microcoil made of a biocompatible metal (preferably platinum or platinum/tungsten alloy), with an optional core in the form of a continuous length of thin, highly flexible metal wire, preferably of a shape memory metal alloy such as Nitinol. Alternatively, the carrier may be a suitable length of flexible wire, cable, braid, or other construction that yields the desired flexibility. The carrier is preferably made of a biocompatible metal so as to be visible by means of X-rays or other visualization techniques known in the art, but it also may be made of a suitable polymer that is visible (or is rendered visible) through any of the known visualization methods. The carrier should have sufficient column strength to allow the device to be pushed through a microcatheter.
In the second preferred embodiment, an elongate, continuous, coaxial embolizing element is non-releasably fixed to the exterior surface of the carrier, extending along a substantial portion of the length of the carrier proximally from a distal tip.
In either of the preferred embodiments, the embolizing elements may be made of a hydrophilic, macroporous, polymeric, hydrogel foam material, in particular a swellable foam matrix formed as a macroporous solid comprising a foam stabilizing agent and a polymer or copolymer of a free radical polymerizable hydrophilic olefin monomer cross-linked with up to about 10% by weight of a multiolefin-functional cross-linking agent. Such a material is described in U.S. Pat. No. 5,750,585xe2x80x94Park et al., the disclosure of which is incorporated herein by reference. The material may be modified, or provided with additives, to make the implant visible by conventional imaging techniques.
In the second preferred embodiment, the elongate coaxial embolizing element is preferably made of a porous, environmentally-sensitive, expansile hydrogel, of the type described in prior co-pending U.S. patent application Ser. No. 09/783,762, assigned to the assignee of this application and of the invention disclosed and claimed herein. Application Ser. No. 09/783,762 (the disclosure of which is incorporated herein by reference) discloses hydrogels that undergo controlled volumetric expansion in response to changes in such environmental parameters as pH or temperature. These hydrogels are prepared by forming a liquid mixture that contains (a) at least one monomer and/or polymer, at least a portion of which is sensitive to changes in an environmental parameter; (b) a cross-linking agent; and (c) a polymerization initiator. If desired, a porosigen (e.g., NaCl, ice crystals, or sucrose) may be added to the mixture, and then removed from the resultant solid hydrogel to provide a hydrogel with sufficient porosity to permit cellular ingrowth. The controlled rate of expansion is provided through the incorporation of ethylenically unsaturated monomers with ionizable functional groups (e.g., amines, carboxylic acids). For example, if acrylic acid is incorporated into the crosslinked network, the hydrogel is incubated in a low pH solution to protonate the carboxylic acids. After the excess low pH solution is rinsed away and the hydrogel dried, the hydrogel can be introduced through a microcatheter filled with saline at physiological pH or with blood. The hydrogel cannot expand until the carboxylic acid groups deprotonate. Conversely, if an amine-containing monomer is incorporated into the crosslinked network, the hydrogel is incubated in a high pH solution to deprotonate the amines. After the excess high pH solution is rinsed away and the hydrogel dried, the hydrogel can be introduced through a microcatheter filled with saline at physiological pH or with blood. The hydrogel cannot expand until the amine groups protonate.
Alternatively, in the second preferred embodiment, the elongate coaxial embolizing element may be in the form of a stretch-resistant outer layer applied to the exterior of the carrier along a substantial portion of the length of the carrier. The stretch-resistant outer layer is preferably formed of an expansile material, such as those described above, but it may also be formed of any stretch-resistant, biocompatible polymer, such as, for example, polyurethane, polyester, polytetrafluoroethylene (PTFE), nylon, polymethylmethacrylate (PMMA), and silicone.
A second aspect of the present invention is a method for embolizing a vascular site, comprising, in the preferred embodiment the steps of: (a) passing a microcatheter intravascularly so that its distal end is introduced into a target vascular site; (b) passing a vaso-occlusive device through the microcatheter into the target vascular site so that the vaso-occlusive device assumes a three-dimensional configuration that fills a portion of the volume of the target vascular site; (c) providing a vascular embolization device comprising at least one expansible embolizing element non-releasably connected to a filamentous carrier; (d) passing the embolization device through the microcatheter so that it emerges from the distal end of the microcatheter into the target vascular site; and (e) expanding the embolizing element or elements in situ so that at least about 30%, and preferably more than about 40%, of the total the volume of the target vascular site is filled, while maintaining the connection between the embolizing element or elements and the carrier.
Preferably, the vaso-occlusive device is of the type that is initially in the form of an elongate, flexible, filamentous element for delivery through the microcatheter, and that assumes a three-dimensional geometry upon installation in the target vascular site. One such device is the above-described GDC (U.S. Pat. No. 5,122,136xe2x80x94Guglielmi et al., the disclosure of which is incorporated herein by reference). Other such devices are describe in, for example, U.S. Pat. No. 5,766,219xe2x80x94Horton; U.S. Pat. No. 5,690,671xe2x80x94McGurk et al.; and U.S. Pat. No. 5,911,731xe2x80x94Pham et al., the disclosures of which are incorporated herein by reference. Still other types of vaso-occlusive devices known in the art may also perform satisfactorily in this method.
In an alternative embodiment of the method of the present invention, the method comprises the steps of: (a) deploying an intravascular device to a position in a blood vessel adjacent to a target vascular site; (b) providing a vascular embolization device comprising at least one expansible embolizing element non-releasably connected to a filamentous carrier; (c) passing a microcatheter intravascularly so that the distal end of the microcatheter passes through the intravascular device into the target vascular site; (d) passing the embolization device through the microcatheter so that it emerges from the distal end of the microcatheter into the target vascular site; and (e) expanding the embolizing element or elements in situ substantially to fill the volume of the target vascular site while maintaining the connection between the embolizing element or elements and the carrier.
It is understood that the step of providing the embolization device may follow the step of passing the microcatheter intravascularly.
In this alternative embodiment of the method aspect of the present invention, the intravascular device may be of the type disclosed in U.S. Pat. No. 5,980,514xe2x80x94Kupiecki et al., the disclosure of which is incorporated herein by reference. This intravascular device comprises a filamentous element that is introduced by a microcatheter to the juncture of an aneurysm or the like, and that then assumes the configuration of a coil adjacent the neck of the aneurysm.
In some instances, the step of passing a vaso-occlusive device or an intravascular device through the microcatheter to the target vascular site may be omitted.
The embolization bodies or elements, in the preferred embodiment, have an initial configuration in the form of small, substantially cylindrical xe2x80x9cmicropelletsxe2x80x9d of small enough outside diameter to fit within the microcatheter. The bodies are hydrophilically expansible into an expanded configuration in which they substantially conform to and fill the vascular site.
The present invention provides a number of significant advantages. Specifically, the present invention provides an effective vascular embolization device that can be deployed within a vascular site with excellent locational control, and with a lower risk of vascular rupture, tissue damage, or migration than with prior art devices. Furthermore, the embolization device effects a conformal fit within the site that promotes effective embolization, and yet its ability to be delivered to the site through a microcatheter facilitates precise and highly controllable deployment. In addition, the essentially filamentous initial configuration of the embolization device, whereby it readily conforms to the interior dimensions of the vascular site, allows it to be used effectively to embolize vascular sites having a wide variety of sizes, configurations, and (in the particular case of aneurysms) neck widths. These and other advantages will be readily appreciated from the detailed description that follows.